How much water you need each day
There is no single number that works for everyone. How much water your body needs depends mostly on your weight, how active you are, and the climate you live in. This calculator uses a simple, widely used reference (about 35 ml of water per kilogram of body weight) and then adds an adjustment for exercise and heat to give you a personalized estimate, shown in liters, in 250 ml glasses, and in milliliters.
Keep in mind that “water” here means all the fluid that reaches your body: plain water plus what you get from tea, soups, fruit, and vegetables.
How to use the calculator
- Enter your weight in kilograms.
- Pick your activity level: sedentary if you barely exercise, moderate for around 30 minutes of exercise, or intense for 60 minutes or more.
- Check the hot climate box if you live somewhere warm or the day is especially hot. This adds an extra 10%.
- Read your result in liters, glasses, and milliliters. Use the button to copy it and save or share it.
The method, step by step
The estimate is built from three parts:
- Base: weight in kg × 35 ml.
- Exercise: add about 350 ml for every 30 minutes of activity (0 ml if sedentary, 350 ml if moderate, 700 ml if intense).
- Climate: if you check heat, the running total is multiplied by 1.10 (10% more).
One glass equals 250 ml, so to turn milliliters into glasses you just divide by 250.
Worked example
A person who weighs 70 kg, is sedentary, and lives in a mild climate:
- Base: 70 × 35 = 2450 ml
- Exercise: +0 ml
- Climate: no adjustment
- Total: 2450 ml = 2.45 L ≈ 9.8 glasses of 250 ml
If that same person did 30 minutes of exercise, they would add 350 ml and reach 2800 ml (2.8 L, about 11.2 glasses).
Quick reference (sedentary, mild climate)
| Weight | Milliliters | Liters | Glasses of 250 ml |
|---|---|---|---|
| 50 kg | 1750 ml | 1.75 L | 7.0 |
| 60 kg | 2100 ml | 2.1 L | 8.4 |
| 70 kg | 2450 ml | 2.45 L | 9.8 |
| 80 kg | 2800 ml | 2.8 L | 11.2 |
| 90 kg | 3150 ml | 3.15 L | 12.6 |
Factors that change your needs
- Exercise: you lose fluid through sweat, so more effort means more to replace.
- Climate and temperature: heat and humidity increase how much you sweat.
- Pregnancy and breastfeeding: both raise fluid needs; follow your doctor’s guidance.
- Fever, vomiting, or diarrhea: these increase losses and call for more fluids.
- Height and body composition: this is why the reference is tied to weight.
Signs you are running low on water
Thirst is the first hint. Other signs of dehydration include dark, scant urine, a dry mouth, headache, tiredness, dizziness, and skin that is slow to bounce back. A practical guide: if your urine is a pale, light yellow, you are usually well hydrated.
Frequently asked questions
Is it really 8 glasses a day?
It is a popular, easy-to-remember rule (8 glasses of 250 ml is 2 liters), but it is not a scientific law. For many people it is a reasonable target, yet your real needs depend on your weight, activity, and climate, which is what this tool estimates.
Do coffee and tea count as fluid?
Yes. Although caffeine has a mild diuretic effect, caffeinated drinks in normal amounts still add net fluid to your body. The same goes for herbal teas, milk, juice, and the water in fruit and vegetables.
Can you drink too much water?
Yes, though it is uncommon. Drinking huge amounts in a short time can dilute the sodium in your blood and cause hyponatremia, which can be dangerous in severe cases. Drink to your thirst and spread your intake through the day instead of forcing down large volumes at once.
Does this calculator replace a doctor?
No. It is an educational estimate. If you have kidney or heart disease, are pregnant, or take medications, check with a healthcare professional to learn the right amount for you.